I'm going to guess you didn't air down enough or hit the rock to hard/fast. If you air down to about 12PSI the tire becomes twice as wide as the rim. This creates a barrier so the rim should of had rubber between it and the rock. Look at my video here fast forward to 1:26 this is aired down to 15-17 PSI I think it was but you can see how much the tire mushrooms out protecting the rim from the rock.